1. Field of the Invention
The present invention relates to a magneto-optical disk apparatus, which can accurately reproduce a signal by removing a magnetic influence applied from a magnet for servo-control of an objective lens for converging laser beams onto a magneto-optical record medium. The present invention also relates to a magnetic field intensity detecting method of detecting an intensity of an influence magnetic field applied from a magnet for servo-control.
2. Description of the Related Art
Magneto-optical record mediums have received widespread attention as record mediums, which are rewritable and have large storage capacities and high reliability, and are being used as computer memories and others. Recently, a magneto-optical record medium having a storage capacity of 6.0 Gbytes is standardized as AS-MO (Advanced Storage Magneto Optical disk) and practical use thereof is starting.
A signal is recorded on the magneto-optical record medium in such a manner that a magnetic head is initially in contact with a surface of a side of the magneto-optical record medium provided with a magnetic layer, and a magnetic field modulated with the record signal (i.e., signal to be recorded) is applied to the magnetic layer of the magneto-optical record medium while floating the magnetic head by rotating the magneto-optical record medium at a predetermined rotation speed. Laser beams are emitted to a side remote from the magnetic head for heating a predetermined region of the magnetic layer of the magneto-optical record medium to or above a predetermined temperature. Thereby, magnetic domains, which are magnetized in different directions in response to the record signal, are formed on the record layer of the magnetic layer to record the signal.
For reproducing the signal from the magneto-optical record medium, the magnetic domains on the regions, which are heated to or above the predetermined temperature by laser beam irradiation, are transferred onto the reproduction layer and the magnetic domains thus transferred are detected as a rotation angle of a plane of polarization of the laser beams. Thereby, the signals are reproduced from the magneto-optical record medium. In this case, the magnetic head is disposed on the side opposite to the side irradiated with the laser beams. When reproducing the signal, the magnetic head is not in contact with the magneto-optical record medium, and is spaced from the magneto-optical record medium.
When the signal recorded on the magneto-optical record medium is to be reproduced such a manner is employed for quick reproduction of the signal that the magnetic head is kept in contact with the magneto-optical record medium, and the side opposite to the magnetic head is irradiated with the laser beams for reproducing the signal.
When the signal is reproduced from the magneto-optical record medium while keeping the magnetic head in contact with the magneto-optical record medium, a magnetic force applied from a magnet, which is used for focus servo-control or tracking servo-control of an objective lens for converging the laser beams onto the magneto-optical record medium, concentrates on a core (made of a magnetic material such as ferrite) of the magnetic head, and thus exerts an adverse effect on the reproduced signal.
Accordingly, an object of the invention is to provide a magneto-optical disk apparatus, which can reproduce signals from a magneto-optical record medium while removing an influence of a magnetic field, which is concentratedly applied to a core of a magnetic head from a magnet performing focus servo-control or tracking servo-control of an object lens.
Another object of the invention is to provide a magnetic field intensity detecting method of detecting an intensity of a magnetic field, which is concentratedly applied to a core of a magnetic head from a magnet performing focus servo-control or tracking servo-control of an object lens.
The invention provides a magneto-optical disk apparatus for recording a signal on a magneto-optical record medium with a laser beam and a magnetic field, and reproducing the signal from the magneto-optical record medium with the laser beam including a magnetic head for applying a magnetic field to the magneto-optical record medium; a lowering device for lowering the magnetic head to a position in contact with the magneto-optical record medium; an optical head disposed on a side remote from the magnetic head with the magneto-optical record medium therebetween, and including an objective lens for converging the laser beam onto the magneto-optical record medium, a first magnet for performing tracking servo-control of the objective lens and a second magnet for performing focus servo-control of the objective lens; and a third magnet for cancelling a leaked magnetic field produced by at least one of the first and second magnets and convergently applied toward the magnetic head.
In the above magneto-optical disk apparatus according to the invention, the magnetic head is lowered by the lowering device, and comes into contact with the magneto-optical record medium. When the magneto-optical record medium turns, the magnetic head floats from the magneto-optical record medium. The third magnet cancels the magnetic influence, which may be exerted on the magneto-optical record medium by the first or second magnets included in the optical head for performing the tracking servo-control of the objective lens or the focus servo-control thereof. While floating the magnetic head from the magneto-optical record medium, recording and/or reproducing of the signal on the magneto-optical record medium are performed. According to the invention, therefore, the recording and/or reproducing of the signal on the magneto-optical record medium can be accurately performed while keeping the magnetic head in contact with the magneto-optical record medium.
Preferably, the third magnet emits the magnetic field of an intensity determined by a magnetic field intensity detecting method using a DC magnetic field, and the magnetic field intensity detecting method includes a first step of irradiating the magneto-optical record medium with the laser beam, and reproducing the signal from the magneto-optical record medium by applying a DC magnetic field in a first direction to a point irradiated with the laser beam while changing an intensity of the DC magnetic field, a second step of detecting the number of errors in the signal reproduced in the first step, a third step of reproducing the signal from the magneto-optical record medium by applying a DC magnetic field in a second direction opposite to the first direction onto the irradiation point, a fourth step of detecting the number of errors in the signal reproduced in the third step, and a fifth step of detecting an intensity of the magnetic field applied from the first or second magnet at the irradiation point based on a relationship between the error numbers detected in the second and fourth steps and the intensities of the DC magnetic fields.
The magnetic head is lowered by the lowering device to make contact with the magnetic-optical record medium. When the magneto-optical record medium turns, the magnetic head floats from the magneto-optical record medium. The third magnet cancels the magnetic influence, which is applied to the magneto-optical record medium by the first magnet for tracking servo-control of the objective lens included in the optical head or the second magnet for the focus servo-control of the objective lens. While keeping the magnetic head in a position floated from the magneto-optical record medium, recording and/or reproducing of the signal on the magneto-optical record medium are performed. The intensity of the magnetic field emitted from the third magnet is determined to be equal to the magnetic field intensity, which is detected based on the relationship between the number of errors in the signal reproduced by applying the DC magnetic field to the magneto-optical record medium and the intensity of the DC magnetic field. According to the invention, therefore, the recording and/or reproducing of the signal on the magneto-optical record medium can be accurately performed while keeping the magnetic head in contact with the magneto-optical record medium.
Preferably, the third magnet of the magneto-optical disk apparatus is arranged in the radial direction of the magneto-optical record medium, and has a length longer than a range of radial movement of the optical head.
When the optical head moves in the radial direction of the magneto-optical record medium in a seek operation or the like, the first and second magnets included in the optical head change their positions. Even in this case, the third magnet removes the magnetic influence exerted by the first or second magnet. According to the invention, therefore, the signal can be accurately reproduced while removing the magnetic influence exerted from the magnet, which is included in the optical head, even when the optical head moves in the radial direction of the magneto-optical record medium.
Preferably, the third magnet of the magneto-optical disk apparatus is arranged on the same side as the optical head with respect to the magneto-optical record medium.
A magnetic flux coming from the first or second magnet included in the optical head enters the third magnet arranged on the same side as the optical head with respect to the magneto-optical record medium. According to the invention, therefore, it is possible to eliminate the magnetic influence by the magnet included in the optical head even if the third magnet is arranged on the same side as the optical head with respect to the magneto-optical record medium.
Preferably, the third magnet of the magneto-optical disk apparatus is arranged on the same side as the magnetic head with respect to the magneto-optical record medium.
The magnetic flux coming from the first or second magnet included in the optical head is cancelled by the magnetic flux coming from the third magnet arranged on the side opposite to the optical head with respect to the magneto-optical record medium. According to the invention, therefore, it is possible to eliminate the magnetic influence by the magnet included in the optical head even if the third magnet is arranged on the side opposite to the optical head with respect to the magneto-optical record medium.
Preferably, the third magnet of the magneto-optical disk apparatus has a plate form having first and second planes, and emits from the first plane the magnetic field for cancelling the leaked magnetic flux caused by the first or second magnet.
The third magnet for eliminating the magnetic influence by the first or second magnet included in the optical head has a plate form, and emits the magnetic flux from the plane of the plate form. According to the invention, therefore, the third magnet for removing the magnetic influence by the first or second magnet included in the optical head can be easily attached.
Preferably, the magneto-optical disk apparatus further includes an outer appearance member for covering a loading portion of the magneto-optical record medium, and the third magnet is arranged on the outer appearance member through the second plane.
Once the position of the third magnet for removing the magnetic influence by the first or second magnet included in the optical head is adjusted, the third magnet will remove the magnetic influence by the first or second magnet. According to the invention, therefore, the magnetic influence by the first or second magnet can be stably removed.
Preferably, the third magnet of the magneto-optical disk apparatus is arranged on the outer appearance member, and a magnetic field leakage preventing member for preventing external leakage of the magnetic field from the second plane is interposed between the third magnet and the outer appearance member.
The magnetic field leak preventing member prevents the external leakage of the magnetic field through the outer appearance member. According to the invention, therefore, the signal is not erased even when the magneto-optical record medium or the like is located near the magneto-optical disk apparatus.
Preferably, the magnetic field leakage preventing member is made of metal.
The magnetic field leakage preventing member prevents the external leakage of the magnetic field through the outer appearance member, and further removes the magnetic influence caused by the first or second magnet included in the optical head so that it enhances the magnetic flux emitted from the third magnet. According to the invention, therefore, a magnet of a small magnetic flux density can be used for removing the magnetic influence by the first or second magnet included in the optical head.
The invention also provides a magneto-optical disk apparatus for detecting an intensity of an influence magnetic field, which is exerted on an irradiation point of a laser beam by a magnet employed for servo-control of an objective lens for irradiating a magneto-optical record medium with the laser beam, recording a signal on the magneto-optical record medium with the laser beam and the magnetic field, and/or reproducing the signal from the magneto-optical record medium with the laser beam. The magneto-optical disk apparatus includes a first magnetic head for applying the magnetic field to the magneto-optical record medium; a lowering device for lowering the first magnetic head to a position in contact with the magneto-optical record medium, an optical head including an objective lens arranged on the side remote from the first magnetic head with the magneto-optical record medium therebetween for converging the laser beam to the magneto-optical record medium, and the magnet; a second magnetic head for cancelling the influence magnetic field; a magnetic head drive circuit for driving said first or second magnetic head; and a control circuit. When detecting the intensity of the influence magnetic field, the control circuit controls the magnetic head drive circuit such that the first magnetic head applies a DC magnetic field in a first direction or a DC magnetic field in a second direction opposite to said first direction to said magneto-optical record medium while changing the intensity of the DC magnetic field. The control circuit determines the intensity of the influence magnetic field based on the number of errors in a reproduced signal detected by the optical head under the DC magnetic field. The magnetic head drive circuit drives the first magnetic head to apply the DC magnetic field to the magneto-optical record medium under control by the control circuit. The optical head detects the signal on the magneto-optical record medium. When producing the signal, the control circuit controls the magnetic head drive circuit to produce by the second magnetic head the magnetic field of the same intensity as the determined intensity of the influence magnetic field. The magnetic head drive circuit drives the second magnetic head to produce the magnetic field of the same intensity as the influence magnetic field under the control by the control circuit.
According to the above magneto-optical disk apparatus of the invention, when the intensity of the influence magnetic field, which is applied from the magnet for servo-control of the objective lens, is to be detected, the control circuit controls the magnetic head drive circuit to produce the DC magnetic field of a changed intensity from the first magnetic head. The optical head reproduces the signal from the magneto-optical record medium under the DC magnetic field, and the number of errors in the reproduced signal is detected. The above operation is performed for the DC magnetic fields in the two directions. The control circuit receives the detected number of errors, and obtains the relationship between the number of errors and the intensity of the DC magnetic field. The control circuit obtains the magnetic field intensity exhibiting a lateral symmetry, and determines the intensity of the influence magnetic field.
When reproducing the signal, the control circuit controls the magnetic head drive circuit to produce by the second magnetic head the magnetic field of the same intensity as the determined influence magnetic field intensity, and the magnetic head drive circuit drives the second magnetic head under the control by the control circuit so that the second magnetic head produces the magnetic field of the same intensity as the influence magnetic field. According to the invention, therefore, the magnetic field for cancelling the influence magnetic field can be produced based on the measured intensity of the influence magnetic field. As a result, the recording and/or reproducing of the signal on the magneto-optical record medium can be accurately performed.
The invention provides a method of detecting a magnetic field intensity for detecting an intensity of a magnetic field applied onto an irradiation point of a laser beam by a magnet employed for servo-control of an objective lens for irradiating a magneto-optical record medium with the laser beam. The method includes a first step of emitting the laser beam to the magneto-optical record medium and simultaneously applying a DC magnetic field in a first direction to the irradiation point while changing the intensity of the DC magnetic field to reproduce the signal from the magneto-optical record medium; a second step of detecting the number of errors in the reproduced signal reproduced in the first step; a third step of applying a DC magnetic field in a second direction opposite to the first direction to the irradiation point to reproduce the signal from the magneto-optical record medium; a fourth step of detecting the number of errors an the reproduced signal reproduced in the third step; and a fifth step of detecting an intensity of an influence magnetic field exerted on the irradiation point by the magnet based on the relationship between the number of errors detected in the second and fourth steps and the intensities of the DC magnetic fields.
According to the above method of detecting the magnetic field intensity of the invention, the laser beam is emitted to the magneto-optical record medium, and the DC magnetic field is applied while changing the intensity on the irradiation point of the laser beam. The number of errors in the reproduced signal is detected. This detection of the number of errors is performed for the cases of applying the DC magnetic fields in the two directions, respectively and the intensity of the influence magnetic field is determined from the relationship between the numbers of errors in the reproduced signal and the intensities of the DC magnetic fields. According to the invention, therefore, the DC magnetic field is applied to the magneto-optical record medium to detect the number of errors in the reproduced signal, whereby the intensity of the influence magnetic field applied from the magnet for servo-control of the objective lens can be easily detected.
Preferably, in the relationship between the detected number of the errors and the intensity of the DC magnetic field, the intensity of the first magnetic field starting increase in number of the errors during increase in intensity of the DC magnetic field in the first direction and the intensity of the second magnetic field starting increase in number of the errors during increase in intensity of the DC magnetic field in the second direction are detected, and the average value between the detected intensities of the first and second magnetic fields is determined as the intensity of the influence magnetic field.
In the relationship between the number of errors in the reproduced signal and the intensity of the DC magnetic field, rapid increase in number of the errors occurs at two values of the DC magnetic field intensity. The two values of the DC magnetic field intensity are detected, and the average value between them is calculated to determine the intensity of the influence magnetic field. According to the invention, therefore, the intensity of the influence magnetic field can be easily and accurately determined.
Preferably, a random data pattern recorded on the magneto-optical record medium is reproduced in the first and third steps.
Since the random data pattern recorded on the magneto-optical record medium is reproduced, and the intensity of the influence magnetic field is determined based on the number of errors in the signal thus reproduced. According to the invention, therefore, it is not necessary to record and reproduce data of a specific pattern used for detecting the intensity of the influence magnetic field on and from the magneto-optical record medium so that the intensity of the influence magnetic field can be easily determined.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.